How does having a rotating plate in a microwave help food to be heated eavenly?

As microwaves are emitted from several different sources in a confined space, the waves are reflected off the internal walls and a interference pattern is formed. There are areas of destructive superstition where the radiation intensity is at the minimum (nodes) and areas of constructive superstition where intensity is at its maximum (anti nodes). This is dependent of the path difference of the waves when they meet. Rotating the food around in the microwaves give a chance for the food to move through theese nodes and anti nodes, helping the food heat eavenly.